The invention relates to a method of preparing polyamide acid type intermediates for processing of semiconductors.
More particularly, it relates to a method of preparing polyamide acid type intermediates to be transformed into polyimide resins which, in turn, are used for processing of semiconductors, such as surface-protecting film of semiconductors or interlayer-insulating film of semiconductors having a multiple layer wiring structure.
Although silicon dioxide has been used for processing of semiconductors, such as surface-protecting film or interlayer-insulating film of semiconductors, in the latter case there being a multiple layers wiring structure, it has such defects to be overcome that cracks tend to develop when the thickness of its film is above 5 .mu.m, or that it has a poor step coverage.
Organic materials, i.a. polyimide resins have been used in an attempt to overcome the above-mentioned defects, aiming at their excellent heat resistance, and as the results, problems such as development of cracks and step coverage have been dissolved.
However, their use has caused other problems. For instance heat resistance of polyimide resins decreases in the presence of a free acid produced by ring cleavage of tetracarboxylic acid dianhydride, thus lowering the reliability of semiconductors.
Further, electrical properties of semiconductors are impaired in the presence of ionic impurities, particularly metal ions contained in polyimide resins.